Spark generator for spectrographic analyses



Dec. 18, 1945. H, CLARK 2,391,225

SPARK GENERATOR FOR SPECTROGRAPHIC ANALYSES Filed Oct. 21. 1943 Inventor: Howard L.Clark,

byZ

His Attorney.

Fatented Dec. 18, 1945 SPARK GENERATOR FOR SPECTRO- GRAPHIC ANALYSES rioward L. Clark, Ballston Lake, N. Y., assignor to General Electric Company, a corporation of New York Application October 21, 1943, Serial No. 507,210 3 Claims; (01. 315-241) circuit diagram illustrating my invention the main or are discharge of the generator takes place at the test gap formed by the spaced electrodes I and 2 constructed of the material whose composition is to be analyzed. Energy for the discharge is supplied from either one of the two capacitors 3, 4, the capacitances of which may be 0.5 and 2 mfd. respectively, depending on the position of the switch 5. For charging whichever capacitor is to be employed I have provided the transformer 8 having the primary 1 which is adapted to be connected to a suitable source of alternating current supply, for example a 115 volt, 60 cycle lighting circuit. The transformer has a plurality of secondaries comprising preferably a single winding provided as shown with a plurality of taps 8 and 9 whereby that part of the winding between the tap 8 and the upper end of the winding constitutes one secondary, that part between the taps 8 and 9 constitutes another secondary, and that part between the tap 8 and I the lower end of the winding constitutes still another secondary. According to the position of the switch 5 either capacitor 3 or capacitor 4 is connected through the half -wave rectifier l0 and the resistor l I, whose resistance may for example be 750 ohms, across the secondary which is between the tap 8 and the upper end of the secondary winding, the voltage of which secondary may for example be 1100 volts. The discharge circuit for the capacitors 3 and 4 comprises the test gap between the electrodes l and 2 and the secondary l2 of the Tesla transformer l3. Across the capacitors 3 and 4 are connected the resistor ll, whose resistance may be 2 megohms to remove (for safety reasons) any charge that may be left on them after using the apparatus and also the small capacitor I 8 whose capacitance may for example be .001 mid. to provide a low impedance path for the high frequency induced in the secondary l2. The above described apparatus provides the power for the are between the test gap electrodes but as the voltage of the charges put into the capacitors 3, 4 is not sumcient to cause a breakdown at the test gap I have provided other means which I shall now describe to produce a leader spark across the test gap.

Connected across that secondary of the transformer 6 which is between the taps 8 and 9 is the capacitor I8 whose capacitance may for example be 4 mid., the resistor 19, whose resistance may for example be 330 ohms, and the half-wave rectifier 20, the arrangement being such that the capacitor l8 and the capacitors 3, 4 receive charges from the transformer 6 durin the same half cycles. The discharge circuit of the capacitor [8 comprises the primary 22 of the step-up transformer 23, whose ratio of transformation may for example be 1 to 10, and the anode-cathode circuit of the grid controlled gaseous discharge device 24. The grid circuit of the device 24 includes in addition to the usual high resistor 25 shunted by the small capacitor 26 the negative bias secondary 0f the transformer 8 comprising that part between the tap 8 and the lower end of its secondary winding. The secondary 28 of the step-up transformer 23, whose ratio of transformation may for example be 1 to 10, has

connected across it the small capacitor 29, whose capacitance may for example be .0025 mfd. and bridged across that capacitor and forming therewith an oscillation circuit is the spark gap 30 and the primary 3| of the aforementioned Tesla transformer l3, whose ratio of transformation may for example be 1 to 5.

With reference now to the operation of the above described apparatus, during the first half cycle of the source voltage at which the rectifiers l0 and 20 pass current a charge is given to one or the other of the capacitors 3, 4 according to the position of the switch 5 and a charge likewise is given to the capacitor l8. As mentioned before the voltage of the charge given to the capacitors 3, 4 is insufilcient to cause the gap between the electrodes l and 2 to break down. The discharge device 24 which controls the discharge of the capacitor l8 and its production of the leader spark across the electrodes I, 2 is rendered nonconducting by reason of the negative bias on its grid. At the following half cycle of the source voltage the bias on the grid of the device 24 changes from negative to positive or at least becomes sufliciently less negative to render the device conducting at which time the capacitor l8 discharges through the primary of the transformer 23. The resulting voltage impulse induced in the secondary of that transformer gives a charge to the capacitor 29, the voltage of which charge is enough to make the gap 30 break down and start oscillations in the primary of the Tesla transformer. These high frequency impulses superposed on the charge voltage of the capacitors 3 or 4 cause a leader spark to appear at the test gap l, 2 which leader is immediately followed by an arc discharge fed from capacitor 3 or 4. The, above sequence of operations described as taking place during a single-cycle of applied voltage is repeated for each following cycle during all of which the resulting intermittent arc between the test electrodes produces a spectrum which is characteristic the particular element or elements of which they are composed.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination a capacitor and a half wave rectifier connected in series to be energized from a source of alternating current supply. a discharge circuit for said capacitor including a spark gap. a second capacitor and a second half wave rectifier connected in series to be energized from said source of supply. a high frequency generator, a

discharge circuit for said second capacitor in-' cluding 'a grid controlled electron discharge device and means responsive to the discharge current passed thereby for energizing said generator, means energized by said source for controlling-the grid circuit of said device, and means connected to said high frequency generator and interposed in series relation in the discharge circuit ofosaid first-mentioned capacitor to said spark gap for inducing a high frequency voltage in said first mentioned discharge circuit from said generator.

2,. In combination a capacitor and a half wave rectifier connected in series to be energized from a source of alternating current supply, a discharge circuit for said capacitor including a spark cuit of said device, and an oscillation circuit con-.

nected tobe energized from the secondary of said transformer and including a series connected spark gap and high frequency winding inductively related to said high frequency winding.

3. A spark generator forispectrographic analysis comprising a supply transformer having a plurality of secondaries, a capacitor and a half wave rectifier connected in series across one of said secondaries, a discharge circuit for said capacitor including a 'test gap and the secondary of a Tesla transformer, a second capacitor and a second half wave rectifier connected lnselies across another of said secondaries whereby both of said capacitors receive a charge during the same half cycles, a discharge circuit for said second capacitor including the primary of a-step-up transformer and the anode-cathode circuit of a grid controlled electron discharge device, another of said secondaries being connected to the grid circuit of said device to supply a hold-oi! bias thereto during the half cycles at which current is supplied to said second capacitor and to supply a tum-on bias thereto during the opposite half cycles,a small capacitor connected across the secondary of said step-up transformer, and an oscillation circuit including said small capacitor, a spark gap. and the primary of said Tesla trans- I former. I

HOWARD L. CLARK. 

